Catalytic steam reforming technology has been widely applied for synthesis gas production from hydrocarbon containing feedstocks such as natural gas. Conventional steam methane reformers (SMR) employ tubular reactors packed with reforming catalysts in the form of pellets or structured catalyst packing. The tubular reactors are most commonly vertically mounted in a parallel arrangement in a furnace. Since the steam reforming process is highly endothermic, external heating sources are required. Burners installed within the furnace housing combust natural gas and other fuel sources such as pressure swing adsorption tail gas recycle to support endothermic reactions within the catalyst filled tubes. The heat generated by the burners is transferred by radiation and convection to the reformer tube outer walls, then by conduction from the outer walls to the inner walls, and then by conduction and convection to the reaction mixture in the reformer tube interior. A portion of the heat absorbed by the tubular reactor is utilized to bring natural gas and steam feeds from their feed temperature in a range of about 500° C. to about 550° C. to reaction temperature in a range of from about 650° C. to about 900° C. in order to achieve the desired hydrocarbon conversion.
Typical reforming catalysts are in particulate form and contain active metals such as nickel that are generally deposited on stable ceramic carriers such as alumina supports. In order to achieve close to equilibrium catalytic conversion and high syngas throughput in reforming reactors, catalyst components are designed to be deposited on high surface area ceramic supports, for example, gamma alumina with surface area above 80 m2/g. At high temperatures and under oxidizing conditions such as in the presence of steam or air, the catalytic activity of reforming catalysts can be degraded by vaporization of active metals, agglomeration of metal sites into large clusters which can significantly reduce surface area, encapsulation of metals in collapsed pores due to sintering of ceramic supports, and formation of inactive spinel crystal structures such as NiAl2O4. Even though high temperature promoters like BaO, La2O3, and YSZ can be added to alumina supports to slow down spinel structure formation, the formation of spinel is inevitable when catalysts are exposed to high temperatures (above about 750° C.) under oxidative environments (air or steam) for long-periods of time. Additionally, localized hotspots and high reformer tube wall temperatures resulting from reduced catalytic activity can jeopardize the metal alloy reformer tube lifetime. Costs to replace catalyst because of catalyst performance degradation significantly increase overall project costs and decrease plant on-stream time.
High temperature steam purging of the reformer tubes has been considered as a solution for SMR system start-ups, idling and shut-downs as well as coking clean-up. However, NiAl2O4 spinel formation in the catalyst bed which results after these processes, requires regeneration back to Ni/Al2O3 at much higher temperatures (e.g., above 1000° C.) whilst the reformer tube is purged with a H2 rich gas stream. A common solution for this problem is to get away from the Al2O3 catalyst support and use materials such as Yttria-stabilized zirconia (YSZ) which are not prone to NiAl2O4 formation, however use of such materials significantly sacrifices catalytic surface area and activity in the bed, especially in SMR process.
Accordingly, it is an objective of the invention to develop a reforming catalyst for synthesis gas production having the benefits of high redox tolerance, coking resistance, high temperature stability, and high catalytic activity that is not prone to deactivation by formation of NiAl2O4 spinel structures at high temperatures under oxidizing conditions. These and other objectives are realized by the novel reforming catalyst of the invention.